https://github.com/zed-industries/zed/tree/633b665379c18a069...
The extension that invokes it isn’t, but there are a few implementations of it that are, and I think vscodium bundles one with their build. It’s just some shell scripts that download the reh build and run it with the correct args.
> The Visual Studio Code Remote Development extensions and their related components use an open planning, issue, and feature request process, but are not currently open source.
https://code.visualstudio.com/docs/remote/faq#_why-arent-the...
Mainly just sets up the UI/connect commands in vscode UI and launched REH (the vscode server) on the remote machine. The actual server is just a different binary you build from the same repo. Non-Microsoft OSS builds of vscode work with SSH fine.